With this research we show that including a subsurface water storage and capillary irrigation system in artificial turf fields can lead to significantly lower surface temperatures compared to conventional artificial turf fields. Lower surface temperatures are important for the health and wellbeing of the players. Additionally, the field’s rainwater retention capacity reduces stormwater drainage, which helps mitigate urban flooding and benefits the overall sustainability of the city.

The most important result is that with circular on-site water management in the field’s foundation (capture -storage – capillary rise) a significant evaporative cooling effect is achieved, reducing heat stress and thus improving the playing conditions and player safety on artificial turf during sunny warm weather.

Increasing population densities in cities result in increased use of outside sport facilities for field sports. However playable hours on natural turf are limited. As a result, the number of fields with artificial turf instead of natural grass is increasing, in cities like Amsterdam. However, artificial turf lacks rainwater retention and evaporative cooling capacity when compared to natural grass, with a negative effect on urban stormwater management and playability in terms of thermal comfort. In this study we investigated the possibilities to reduce these negative effects through evaporative cooling using (rain-)water, based on circular and on-site water management in the field’s subbase. 

Directly underneath the synthetic turf and shockpad an 85 mm open water storage layer  (Permavoid 85s retention system) in which rainwater is stored. Within the retention system, capillary cylinders of hydrophilic rockwool fibers transport retained water back up to the capillary shockpad made from the same hydrophilic fibers, through the artificial turf backing to the sand infill, where the water evaporates, reducing the surface temperature. The process of evaporative cooling and capillary rise is not controlled by field managers, but by natural processes and weather conditions, so water only evaporates when there is demand for cooling. The main source of water is rain, but in case of prolonged dry periods extra water from other sources can be automatically (sensor-controlled) added to the system.

We found lower temperatures at 75 cm above the cooled plots compared to conventional artificial turf fields, especially during the night. This is a first indication that the cooled plots contribute less to the urban heat island effect, compared to conventional artificial turf. However, the plots were relatively small, so it was not possible to quantify this effect on an urban scale. More research with larger fields is needed to determine how significant the difference is.

During extended dry periods, extra water needs to be added to the system to retain its cooling abilities. The easiest way is to add water directly into the subbase water retention system, but excess water from conventional spray applications would also drain into the retention system for storage and later re use.

A capillary-cooled, stormwater-managing synthetic turf field requires an initial investment of 25% to 100% more than a conventional synthetic turf pitch, depending on the required or desired stormwater attenuation volume. A comprehensive cost-benefit analysis or life cycle assessment (LCA) is necessary to compare the two options. This analysis should consider all benefits, including increased playable hours, health benefits, reduced construction depth and material transport, urban heat island reduction, and improved stormwater management, to determine the true value of the investment.

Heat on synthetic turf has long been an issue which could not be solved with above ground spray application of water, because of the required regular re-application of (drinking-) water and the negative effect of just-wetted synthetic turf on the play characteristics of the pitch (slippery). With this work we show the benefits of the subsurface water storage and capillary irrigation, with sufficient water retention capacity to sustain cooling, based on rainwater and without changing or affecting the playing conditions of artificial turf fields

Most of all, people in urban areas, especially children, have a growing need for sport and play facilities. It is our task to provide a safe, reliable and cool environment for them to play sports in, without health risks associated with the high surface temperatures, like overheating or burns.

The results of this project in which the city, the industry, research and local stakeholders truly cooperated in science and demonstration, has already lead to the system being installed in other countries such as Japan and the United Kingdom.

Yes it did, since releasing the CitySports paper various cooling field installations have been installed:

• Sportheldenbuurt Amsterdam, two fields in the middle of a recently developed urban area
• Middenmeer, a training field at nature inclusive sports park Middenmeer in Amsterdam. 
• HC Athena, a fullsize hockeyfield in Amsterdam. 
• CKV Rapid, Haarlem
• De Ster, Den Haag 
• Rooftop fields in the city of London
• Training field at Kobe, Japan
• Two full size fields at two high schools in Kobe, Japan

For more references, please visit www.dutchblue.world/projects and www.permavoid.com/projects

The City of Amsterdam joined forces with the City of Haarlem and SRO and introduced the tender "Scale Up Future Proof Synthetic Turf Pitches" where they will renovate and install 270 sustainable synthetic turf pitches in the next 8 years, supported by a EU LIFE program. More information available here